Reflecting their political philosophies, President Barack Obama and Republican challenger Mitt Romney take sharply divergent paths when it comes to taxing individuals and corporations.

Their basic approach is easy to distinguish: Obama wants to raise taxes on the wealthiest Americans; Romney would slash rates across the board.

But many key details – for Romney’s plan in particular – are lacking and make side-by-side comparison a challenge. And experts warn that neither plan appears sustainable, as they wouldn’t scratch the nation’s mounting deficit unless they’re offset by other tax hikes or matched by sweeping cuts in spending.

“The biggest flaws are that at some point we need to be talking about not looking for more and more tax cuts, we need to talk about how to get the revenue to pay for our spending promises,” said Joshua Gordon, policy director at the nonpartisan Concord Coalition, which advocates fiscal responsibility. “The fiscal challenges over the long term are too much to deal with just on the spending side.”

Here’s what each proposes to do:

INCOME TAXES

Income taxes are about to increase for all Americans when the George W. Bush-era tax cuts expire on Dec. 31. The two candidates differ on what to do.

– Enact a 30 percent minimum tax on all income in excess of $1 million.

The focus of Obama’s plan is to extend tax cuts for the middle class and to raise taxes on higher incomes, what he calls an issue of fairness.

He could raise taxes, though, on incomes below $200,000. Most notably, he’s likely to agree to let a temporary 2 percentage point cut in the payroll tax expire as scheduled on Dec. 31. That would raise every American’s taxes, regardless of income.

Treasury Secretary Tim Geithner signaled in recent congressional testimony that the administration is unlikely to push for an extension of the payroll tax cut for individuals. However, Obama’s stalled jobs bill does propose a payroll tax holiday for most small businesses if they add jobs or raise wages.

Romney wants to:

– Extend the Bush-era tax cuts for all incomes.

– Cut all income tax rates by another 20 percent.

– Limit some deductions so higher income taxpayers still pay the same despite the cut in tax rates.

– Repeal the Alternative Minimum Tax.

– End taxes on capital gains, interest and dividends for incomes below $200,000.

Generally, Romney looks to tax cuts and tax simplification to put more money in people’s pockets and help boost economic growth. They could, however, add to the annual budget deficits and the accumulating debt more than Obama, which could be a drag on growth.

By themselves, the cuts in tax rates would give the biggest break to wealthier Americans, who pay more in taxes.

Those making more than $600,000 would save about $150,000 and those at the very top – making nearly $3 million – would get a $725,000 break, according to the nonpartisan Tax Policy Center.

For households earning between $70,000 and $120,000, the average savings would be about $2,000. Those making between $40,000 and $70,000 would save about $800. The bottom 20 percent – those making less than $20,000 – would see their average federal tax rate increase $149.

Comparing the two candidates on income taxes carries a giant asterisk.

Romney pledges to make his plan “revenue neutral” and says the wealthy would continue the same share of the government’s total tax collection. But he’s refused to identify which tax breaks he’d target to balance the books, and experts with the Tax Policy Center said that makes a side-by-side comparison impossible.

The center said there aren’t enough tax breaks for the wealthy for Romney to target and that he’d be unable to keep his promise to keep his plan revenue neutral without eliminating tax breaks for the 95 percent of households with incomes under $200,000.

“The details are so sparse, it is impossible to figure out whether they can achieve their goals, especially Romney,” said David Kautter, managing director of the Kogod Tax Center at American University.

Romney’s campaign rejects the policy center’s report, and Romney during last week’s presidential debate insisted that he wouldn’t raise taxes on the middle class or grow the deficit.

Before the debate, Romney floated the idea of a cap on income tax deductions to pay for lost revenues. The principle is something Obama has also entertained, but there has been little interest on Capitol Hill, analysts say. In an interview with a Denver TV station, Romney suggested up to a $17,000 limit for families, though his campaign says he’s not necessarily endorsing the approach.

CORPORATE TAXES

Romney would repeal the corporate alternative minimum tax, cut the corporate tax rate from 35 percent to 25 percent, make a research tax credit permanent and switch to a “territorial tax system,” so that profits earned abroad by U.S.-based multinationals would not be subject to U.S. taxes.

Obama would “go in the exact the opposition direction,” said Kautter, adding that Obama would try to expand the existing worldwide system of taxing U.S. corporations, provide incentives for them to move jobs back to the U.S. and penalize companies that try to move jobs offshore.

Obama would cut the corporate rate, though not as deeply. He’d cut it to 28 percent for some. For domestic manufacturers, he’d cut the tax rate to 25 percent.

Obama also would eliminate a number of oil and gas preferences in the tax law, along with reducing the depreciation for corporate aircraft.

ESTATE TAX

Under the temporary Bush-era tax cuts, estates worth less than $5 million – $10 million for couples – are exempt from the tax, which can take 35 percent for Uncle Sam.

On Jan. 1, however, the tax shoots back up to its old levels, hitting estates valued at $1 million or more and assessing a top rate of 55 percent.

Romney proposes to repeal the estate tax, which is paid by a small number of wealthy families.

Obama would split the difference. He’d exempt estates worth less than $3.5 million – $7 million for couples – and set the top tax rate at 45 percent – the same levels that were in effect in 2009.

The Tax Policy Center has concluded that for households earning between $70,000 and $120,000, Obama’s plan would pay about $71 more in taxes. Those making between $40,000 and $70,000 would save about $11.

The biggest earners would be hardest hit: Those making more than $600,000 would see about an increase of about $100,000, and those at the very top – making nearly $3 million – would see a $549,000 increase.

The bottom 20 percent – those making less than $20,000 – would see their average federal tax rate fall by $2.